メソッド、パラメータ、オーバーロードはどのように機能しますか？

public int Add(int a, int b) => a + b;          // expression-bodied (concise)

public string Greet(string name, string greeting = "Hello")   // default parameter
{
    return $"{greeting}, {name}";
}
Greet("Ann");                       // "Hello, Ann"
Greet("Ann", greeting: "Hi");        // named argument

// ref — pass by reference (method can modify the caller's variable)
void Increment(ref int x) { x++; }
int n = 5; Increment(ref n);   // n is now 6

// out — for returning multiple values (must be assigned in the method)
bool TryParse(string s, out int result) { result = ...; return true; }
if (int.TryParse("42", out int value)) { }   // the common TryX pattern

// in — pass by reference but READ-ONLY (performance for large structs)
void Process(in LargeStruct data) { }

// params — variable number of arguments
int Sum(params int[] numbers) => numbers.Sum();
Sum(1, 2, 3, 4);    // any number

// OVERLOADING — same name, different parameters
void Print(int x) { }
void Print(string s) { }
void Print(int x, int y) { }
Print(5);           // calls the int version — resolved by argument types